1. Field of the Invention
The present invention relates generally to an apparatus and method for recovering (concealing the loss of) voice packets. More particularly, the present invention relates to an apparatus and method for determining whether a voice packet received at a relay is lost and if the voice packet is lost, recovering (concealing the loss of) the voice packet before relaying the voice packet to a receiver.
2. Description of the Related Art
Voice over Internet Protocol (VoIP) is Internet telephony that sends voice packets over a packet network designed for data communications. VoIP is a communication technology that enables a call to be performed as in a regular phone by converting voice data into IP packets.
In a VoIP communication network, a transmitter converts a voice Pulse Coded Modulation (PCM) signal into compressed voice parameter information using a voice encoder constructed based on a human voice generation model and stores the voice parameter information in packets, prior to transmission to a receiver. The receiver extracts the voice parameter information from the voice packets and reproduces the PCM signal using the extracted information. Since packet transmission is carried out asynchronously in the VoIP communication network, the voice packets do not arrive at the receiver in a consistent manner. If a large number of packets arrive around a particular time, they may be lost. Also, in a mobile communication environment, a bad channel status can lead to packet loss.
Accordingly, recovering of lost packets is a necessary task to be performed by the receiver. Generally, Packet Loss Concealment (PLC) is used to recover the lost packets. Existing PLC techniques basically use the voice information of adjacent normal packets. If only voice information of a previous normal packet is used, a lost packet can be recovered to a certain extent without adding to a packet transmission delay. However, the use of the voice information of both previous and following packets more effectively recovers the lost packet. Unfortunately, the packet transmission delay increases with the number of following packets used to recover the lost packet and thus, the number of packets used needs to be controlled according to a packet transmission time and service requirements.
For further illustration, a conventional voice packet communication environment in the case where the transmitter and the receiver use the same type of audio Coder-Decoder (CODEC) will be described in detail below.
FIG. 1 is a block diagram of a conventional voice packet communication system. Referring to FIG. 1, the voice packet communication system comprises a transmitter 110, a relay 130, and a receiver 150.
The transmitter 110 has a voice packet generator 112 and outputs a voice packet generated from the voice packet generator 112 on a first channel 120. The relay 130, which can be a gateway or a Base Station (BS), outputs the voice packet received from the transmitter 110 on a second channel 140 using a bypass block 132. When the transmitter 110 and the receiver 150 use the same type of audio CODEC, the bypass block 132 outputs the voice packet without any additional processing, to the receiver 150. The receiver 150 recovers the voice packets that may be lost during transmission on the channels 120 and 140, and converts the voice packets to an analog voice signal using a voice packet recovery and output block 152.
As described above, in the case where the transmitter and the receiver use the same kind of audio CODEC and thus, the relay simply bypasses a received voice packet, it is difficult to improve the performance of the packet recovery block in the receiver unless the receiver is a new product, such as a terminal or an IP phone. However, even though voice packet recovery devices and methods have been improved, their features are not applicable to conventional receivers in real implementation. Consequently, users of conventional receivers may not receive services with better voice quality.
Voice packet recovery in the voice packet recovery block 152 has a number of drawbacks, including the following.
First, recovery of a lost voiced packet may be recovered using a previous unvoiced packet. For example, when voiced packets follow an unvoiced packet, that is, when an unvoiced-voiced transient area exists, loss and noise information in the first of the voiced packet is recovered using the previous unvoiced packet.
Second, with the conventional voice packet recovery, when a plurality of packets are contiguously lost, buzz may be output because they are recovered using the voice information of a previous packet.
Third, voice waveforms may become bigger in the process of deriving a lost packet from a previous packet.
Accordingly, a need exists for a system and method for more effectively and efficiently recovering voice packets.